The present invention relates to a spring-loaded intervertebral disk implant for stabilizing two adjacent vertebrae. More specifically, the present invention relates to rectangularly-shaped disk implants which are expanded in the middle portion and are used as an alternative to spinal fusion.
Treatment of a herniated disk in the neck and in the lumbar region continues to be a challenging field of medicine. The classical treatment for a ruptured disk is diskectomy, i.e., removal of the disk from between the vertebrae. In this process, all or a portion of the intervertebral disk is removed, leaving a defect that may bother the patient throughout the rest of their life and compromising the normal interaction between disk and adjacent vertebrae. A procedure that is sometimes used as an alternative is to replace the disk space with a bone graft, usually bone chips cut from the patient's iliac crest, bringing about fusion of the vertebrae above and below the disk, eliminating the empty space between the vertebrae.
Diskectomy with fusion is not ideal because the replaced bone does not have the function of the cartilaginous tissue of the disk, i.e. no cushioning effect, and has complications because of several factors. First, conventional bone plugs used to pack the disk space do not conform to the space of the disk because the disk bulges maximally in the center. The disk space is wider in the middle and narrower at its anterior and posterior ends. For this reason, many commercially available bone plugs have four contact points, i.e. two at each of the front and back of the disk space. Secondly, access to the disk is from the side of the dorsal spine of the adjacent vertebrae, leaving a space that is “off-center” relative to the bodies of the adjacent vertebrae such that the stability of the implant is even more problematical than might be apparent from the limited contact resulting from the shape of the intervertebral space. Another complication is the possibility of infection or other conditions that may require removal of the implant. Also, if the bone pieces do not fuse, they may eventually extrude out of the disk space, pressuring the nerve roots. The most significant disadvantage is that fusion eliminates all motion at the joint between the two vertebrae, as well as the shock-absorbing/cushioning function of the disk.
Various prosthetic disk plugs, or implants, are disclosed in the art, but all are characterized by limitations of not conforming to the shape of the disk space, lack of stability when inserted off-center, inability to be removed, or other disadvantages. For instance, U.S. Pat. No. 4,863,476 (and its European counterpart, EP-A-0260044) describes an elongated body divided longitudinally into two portions having a cam device movable therebetween for increasing the space between the two body portions once inserted into the disk space. However, that device is generally cylindrical in shape such that the only contact points between the device and the vertebral bodies are at the front and back of the disk space, creating increased likelihood of instability and generally rendering that device unsuitable for use after partial diskectomy.
The art also discloses intervertebral disk prostheses such as U.S. Pat. Nos. 3,867,728, 4,309,777, 4,863,477, 4,932,969, Applicant's own U.S. Pat. No. 5,123,926, and French Patent Application No. 8816184 that may have more general contact with the adjacent disks, and spinal joint prostheses as described in U.S. Pat. No. 4,759,769, but which are not intended for use in fusion of the disks. However, the utility of such devices is also limited by a number of disadvantages, in particular, the same lack of cushioning described above in connection with prior art disk plugs and implants. Further, those implants and prostheses that attempt to address this cushioning problem have generally failed because they are not capable of supporting the load imposed upon them by the active post-surgical patient. Further, many prior implants and prostheses require removal of the disk. Removing the disk is not totally undesirable because removing the intervertebral disk does help prevent problems from recurrent disk herniation through the opening into the intervertebral disk space. However, as with all surgical procedures, it is desirable to utilize as much existing structure as possible and to minimize invasiveness. One reason it is desirable to retain as much of the original disk as possible is that if an implant subsequently fails, or if further surgical intervention is indicated for reasons such as infection, the only alternative that is generally available after removal of the intervertebral disk is fusion.
There is, therefore, a need for a device capable of stabilizing the vertebrae adjacent an intervertebral disk that overcomes the various disadvantages and limitations of spinal fusion procedures and the disk plugs and implants that are used in such procedures, and it is an object of the present invention to provide apparatus and methods for meeting that need.
There is also a need for a device that overcomes the disadvantages and limitations to of prior intervertebral disk prostheses and so it is also an object of the present invention to provide apparatus and methods for meeting that need.
There is also a need for a device that can be implanted into the disk space in a procedure that decreases the likelihood of recurrent disk herniation and it is also an object of the present invention to provide apparatus and methods for meeting that need.
There is also a need for a device that combines the function of the disk by retaining as much of the undamaged disk as possible, and by functioning in a similar manner to provide the cushioning effect of the disk, and it is an object of the present invention to provide apparatus and methods for meeting that need.
There is also a need for a device that not only functions to provide the cushioning effect of the intervertebral disk but that also provides the opportunity for the repair of the remaining portion of the disk, and it is an object of the present invention to provide apparatus and methods for meeting that need.
Another need that is apparent from the limitations and disadvantages of prior procedures, disk plugs, and prostheses is the need for a device that maintains the function of the intervertebral disk when implanted between adjacent vertebrae and that is capable of being implanted in a surgical procedure that is minimally invasive and that does not require removal of the entire intervertebral disk, and it is therefore also an object of the present invention to provide apparatus and methods for meeting that need.
Another need that is apparent from the limitations and disadvantages of prior procedures, disk plugs, and prostheses is the need for a device that works with the structure of the intervertebral disk space to maintain as much of the normal function of the disk as possible, and it is also an object of the present invention to provide apparatus and methods that combine the properties of cushioning that can be obtained by utilizing the remaining portion of the disk, stability by utilizing a metal implant, shock absorption by biasing a portion of an insert into engagement with the adjacent vertebrae, a hydrogel that functions to fill gaps in the disk space and to help reconstruct and/or prevent recurrent herniation of the remaining portion of the disk, and if necessary, a medical grade adhesive that helps to hold the remaining portion of the disk together and/or bond the hydrogel to the disk material and/or seal off the opening into the disk space, thereby meeting that need.
Another need that is apparent is the need for a device that is capable of supporting the load imposed upon it when implanted in the disk space while also providing the cushioning function of the natural intervertebral disk and it is also an object of the present invention to provide apparatus and methods for meeting that need.